Comparative cytotoxicity of angiotensin-converting enzyme inhibitors in cultured rat hepatocytes.

Captopril and enalapril, angiotensin-converting enzyme inhibitors (ACEIs), have been associated with idiosyncratic hepatotoxicity. Such drug reactions may be caused by the formation of reactive metabolites by cytochrome P450 isozymes, which can then cause direct or immune-mediated toxicity. Previously, we have demonstrated that enalapril cytotoxicity in primary cultures of rat hepatocytes was due, at least in part, to cytochrome P450-dependent metabolism, and that glutathione was involved in the detoxification process. In the present study, we extended our investigations into mechanisms of cytotoxicity, using rat hepatocyte cultures, to captopril and three recently marketed ACEIs: fosinopril, lisinopril and quinapril. After 24 hr of exposure to lisinopril or enalaprilat (the deesterified metabolite of enalapril), hepatocytes did not show any evidence of cytotoxicity, measured by lactate dehydrogenase leakage, even at 10 mM drug concentrations. The other ACEIs were toxic to the liver cells, with the rank order of toxicity as quinapril (LC50 = 0.28 mM) > fosinopril (LC50 = 0.4 mM) > enalapril (LC50 = 2.0 mM) > captopril (LC50 = 20 mM). In vivo pretreatment of rats with pregnenolone-16 alpha-carbonitrile to induce isozymes of the P450 3A subfamily significantly enhanced the cytotoxicities of quinapril, fosinopril and enalapril but did not affect captopril cytotoxicity. Pretreatment with P450 inducers selective for other isozyme subfamilies (ethanol, beta-naphthoflavone and phenobarbital) did not alter the in vitro toxicity of any of the ACEIs. Co-incubation with SKF525-A (15 microM) or troleandomycin (0.1 mM) reduced the hepatocidal toxicities of quinapril, fosinopril and enalapril. Preincubation with buthionine sulfoximine (2 mM) enhanced the cytotoxicities of quinapril, fosinopril, enalapril and captopril. The results of this study indicate that like enalapril, quinapril and fosinopril can also undergo P450 3A-dependent bioactivation and require maintenance of glutathione status for detoxification, and that captopril causes cytotoxicity independent of cytochrome P450 metabolism.